Method of identifying a caller with a telephone service operator

ABSTRACT

A method of identifying a caller with a telephone service operator. Of the invention, said method comprises the following steps: for the operator, drawing up a list of literal expressions and allocating the caller an identifier consisting of a combination of consecutive literal expressions taken from each of said lists, for the caller, connecting to said telephone service and speaking, in order, each literal expression of said combination, and for the operator, identifying the caller by using voice recognition to search for the combination of literal expressions allocated to the caller. Application to secure access to telephone services.

[0001] The present invention relates to a method of identifying a callerwith a telephone service company. It also relates to a prepaid telephonecard for implementing the method.

[0002] The invention finds a particularly advantageous application inthe field of secure access to telephone services.

[0003] In the remainder of this description, the expression“identification of a caller” refers either to identifying the caller assuch or to identifying a telephone account of the caller to which theamount due for telephone calls is debited, whether the account be aprepaid account or a deferred debit account.

[0004] At present, for telephone services that necessitateidentification of the caller, the latter enters in DTMF code a number ofdigits that varies depending on the type of service and on the telephoneservice company. The number of digits to be entered is generally from 10to 20. However, in the case of a call made with an electronic microchiptelephone card from a public telephone fitted with a card reader, thenumber of digits to be entered is reduced to the four digits of apersonal identification number, because the number of the card is storedin the microchip and is recovered by the telephone and transmitted tothe telephone service company over the network.

[0005] The ergonomics of that prior art method are somewhat limitedbecause the caller must memorize a series of digits, which can be verylong, and so a first improvement has been introduced that consists inre-using the caller's fixed or mobile telephone number, to which apersonal identification number can be added.

[0006] That solution is particularly suitable for services accessed fromthe caller's main telephone installation, whose number is transmittedautomatically by the network.

[0007] In the case of mobile services, that solution removes thedifficulty of memorizing identification numbers, as a caller generallyknows his own telephone number, but does not avoid the need to enterdigits in DTMF code.

[0008] Prepaid cards also employ that solution, by means of the facilityfor associating a prepaid card with a given telephone line, usually theone that the user employs most often to make calls using the card.

[0009] The above-described identification method is satisfactory in thecase of access to telephone services from a fixed or a mobile terminal,in which case the identifier of the caller consists of the telephonenumber associated with the terminal, possibly with the addition of apersonal identification number.

[0010] Nevertheless, in a mobile situation, the ergonomics remainsomewhat irksome as the caller must still make a long and evenpainstaking (to avoid miskeying, etc.) entry in DTMF code, notforgetting that the user also has to remember his personalidentification number.

[0011] Finally, for some services security is limited as the caller'stelephone number is often known to third parties, so that a fraudsterneeds only to discover the personal identification number, if there isone.

[0012] A caller must still enter the entire number if using his prepaidtelephone card at a telephone that is not associated with the card, aswhen making a call from a public telephone or away from home.

[0013] This phase is particularly difficult for prepaid cards, since forsecurity reasons the number cannot be personalized. As a series of morethan ten digits is generally very difficult to remember, the user mustkeep the card on his person at all times and take it out each time acall is made, in order to enter its number.

[0014] Accordingly, the technical problem to be solved by the presentinvention is that of identifying a caller with a telephone servicecompany by a method that has improved ergonomics compared to the priorart method, in particular with regard to memorizing the identifier,while enhancing security.

[0015] The solution of the present invention to the technical problemthus stated consists in a method that comprises the following steps:

[0016] for the telephone service company, drawing up a list of literalexpressions and allocating to the caller an identifier consisting of acombination of consecutive literal expressions taken from each of saidlists,

[0017] for the caller, connecting to said telephone service andspeaking, in order, each literal expression of said combination, and

[0018] for the telephone service company, identifying the caller bysearching a database for the identity of the caller allocated thecombination of literal expressions spoken by the caller and recognizedby the company.

[0019] The identification method of the invention is therefore based onvoice recognition, for which existing technologies, in particularflexible multi-speaker voice recognition, are already able to recognizea spoken literal expression from among several thousand, the onlycondition being that it must be known which list contains the literalexpression to be recognized. Generally speaking, a literal expressioncomprises a single word or a meaningful set of words, such as“Everything is OK”.

[0020] In the case of a non-personalized service, such as a prepaidtelephone card, an identifier corresponds to a card.

[0021] Compared to spoken or DTMF code entry of a multidigit identifier,the advantages of an identification method of the invention using voicerecognition of a combination of literal expressions are:

[0022] it is faster, a few seconds being sufficient to speak a series ofliteral expressions, and

[0023] it is easier to remember, provided that the literal expressionsare carefully chosen, of course, thereby enabling the caller to use theservice without having his identifier on his person.

[0024] An identification method of the invention can be made secure intwo ways.

[0025] A first way is to increase the number of potential combinationsof literal expressions and allocate a limited number of suchcombinations as identifiers. If all possible combinations of literalexpressions are known, the security ratio is the ratio of the number ofpossible combinations to the number of identifiers actually allocated.The hypothesis that all potential identifiers are known is much lessprobable with literal expressions than with digits, as the vocabulary isricher than the number of digits, which is limited to 10. Of course, thenumber of possible combinations can be further increased by increasingthe number of lists of literal expressions used to formulate theidentifier.

[0026] In a second security mode conforming to the invention, anauthentication key is associated with the identifier and the callerprovides the authentication key after speaking the combination ofliteral expressions allocated to him.

[0027] There are several variants of the authentication key associatedwith the identifier.

[0028] In a first variant, the authentication key is a number of digitsto be entered in DTMF code.

[0029] In a second variant, the authentication key is another literalexpression recorded by the caller the first time he connects to thetelephone service.

[0030] In a third variant, the authentication key is a voiceprint of thecaller established on speaking the combination of literal expressions.

[0031] Finally, associating a double authentication key with theidentifier can be envisaged, comprising a main key consisting of avoiceprint and a back-up key consisting of a plurality of digits to beentered in DTMF code. This advantageous feature remedies situations inwhich the voiceprint of the caller cannot be recognized (for examplebecause the caller is hoarse). In this case, the telephone servicecompany, having determined that it is impossible to recognize the mainkey, requires the caller to provide his back-up key.

[0032] In a particular implementation callers may be provided with thefacility to deactivate the authentication key, which reduces securitybut improves ergonomics.

[0033] The following description with reference to the accompanyingdrawings, which are provided by way of non-limiting example, explains inwhat the invention consists and how it can be put into effect.

[0034]FIG. 1 shows a first method of formulating an identifierconforming to an identification method of the invention using two listsof literal expressions.

[0035]FIG. 2 shows a variant of FIG. 1 in which the second list isdivided into categories.

[0036]FIG. 3 shows a second method of formulating an identifierconforming to an identification method of the invention using threelists of literal expressions.

[0037]FIG. 4 is a diagram showing an implementation of an identificationmethod of the invention using a prepaid telephone card.

[0038] Implementations of a method in accordance with the invention ofidentifying a caller with a telephone service are described below withreference to FIGS. 1 to 3.

[0039] They are all based on the capabilities of existing voicerecognition systems to recognize a word in a list of N words, where N isof the order of several thousand, and have in common the followingsteps:

[0040] for the telephone service company, drawing up at least one listof literal expressions and allocating to the caller an identifierconsisting of a combination of consecutive literal expressions takenfrom each of said lists,

[0041] for the caller, connecting to said telephone service andspeaking, in order, each literal expression of said combination, and

[0042] for the telephone service company, identifying the caller bysearching a database for the identity of the caller allocated thecombination of literal expressions spoken by the caller and recognizedby the company.

[0043] The FIG. 1 embodiment corresponds to the use of an identifierresulting from combining two literal expressions, or words, takensuccessively from two lists drawn up beforehand, one example of which isshown in FIG. 1.

[0044] If each list includes 3000 literal expressions, so that 6000literal expressions must be defined for the two lists, taking allpossible pairs of the literal expressions contained in the two listsproduces a total of 9,000,000 identifiers.

[0045] The total number of identifiers actually used can greatly exceedthe above number, especially if the identifiers are associated withcirculating prepaid telephone cards, the number of which can greatlyexceed a few tens of millions; in this case, it is all possibleword1/word2 combinations that form the set of recognized identifiers.

[0046] However, in the fight against fraud, this solution has thelimitation that all word1/word2 pairs are valid a priori. By purchasinga card A and a card B, a would-be fraudster could obtain two new validcombinations, namely “word 1 card A+word 2 card B” and “word 1 cardB+word 2 card A”.

[0047] To prevent all possibility of fraud, it is advantageous toprovide a complementary authentication key with the identifier of thecaller. Each word1/word2 combination is then authenticated by anauthentication key.

[0048] The authentication key can be four digits to be entered in DTMFcode, another literal expression recorded by the caller the first timehe connects to the telephone service, or a voiceprint that isestablished during the first few calls on the basis of the spokencombinations of N words constituting the identifier of the caller. Forexample, as soon as the voiceprint is considered to be sufficientlyreliable, voice authentication is activated and substituted for thedigits entered in DTMF code. Authentication is then effected bycomparing the voiceprint of the sound signal heard during identificationwith the stored voiceprint.

[0049] For improved ergonomics, there can be provision for the caller todeactivate the authentication key.

[0050]FIG. 2 shows an embodiment using an identifier with only two listsof literal expressions, as in FIG. 1, but in which the security of themethod is enhanced by using the category concept. To be more precise, acategory n is associated with each literal expression in a first listand each category n is associated with a second list of literalexpressions from which the next literal expression is taken.

[0051] Thus the number of potential identifiers can be greatly increasedand security greatly enhanced without degrading the ergonomics, i.e.still limiting to two the number of literal expressions constituting theidentifier.

[0052] In the FIG. 2 embodiment, when word 1 in list 1 has beenrecognized, the category n associated with word 1 is determined.Finally, word 2 is looked for in list 2 associated with category n.

[0053] The valid combinations are thus the pairs “word 1 category n list1+word 2 list 2 associated with category n”.

[0054] Clearly, unlike the previous situation, if a fraudster were topurchase two prepaid cards A and B, he could not be sure that thecombinations “word 1 card A+word 2 card B” and “word 1 card B+word 2card A” would be valid.

[0055] Taking 5000 literal expressions for the first list and fivecategories of second lists, each of 2000 literal expressions, 10,000,000combinations are obtained by defining 15,000 expressions for the variouslists.

[0056] Of course, an authentication key as defined above can beassociated with the identifier determined as shown in FIG. 2.

[0057]FIG. 3 illustrates an embodiment in which a high level of securityis obtained by a large number of possible combinations, greater than thenumber of valid identifiers.

[0058] To be more precise, the identifiers that can be allocated tocallers consist of a combination of three successive literal expressionseach taken from one of three lists of literal expressions drawn upbeforehand.

[0059] In the case of prepaid cards, by purchasing a card A and a card Ba fraudster could potentially obtain six new combinations that might bevalid, namely “word 1 card A+word 2 card A+word 3 card B”, “word 1 cardA+word 2 card B+word 3 card A”, etc.

[0060] A probability calculation shows that a total of 125,000,000,000combinations is obtained by defining 5000 literal expressions per list.Also, if the installed base of cards contains 10,000,000 units, it canbe deduced that the probability of a person who knows all 5000 wordsfinding a valid combination is one in 12,500 on each attempt.

[0061] Since in practice it seems very improbable that a person couldknow all the literal expressions, the security of the FIG. 3 embodimentis maximized.

[0062]FIG. 4 shows how the identification method of the invention can beimplemented when using a prepaid telephone card.

[0063] The prepaid card includes, in an area to be scratched off, anidentifier consisting of one or more literal expressions to be spoken bya purchaser to identify himself with a telephone service company by anidentification method of the invention. By way of redundancy, the cardcan also include, in another area to be scratched off, a multidigit codeto be used if voice recognition is not possible (for example in a noisyenvironment). Similarly, the card can further include an authenticationkey.

[0064]FIG. 4 shows the following steps:

[0065] 1. The purchaser of the card enters a service access prefix (forexample 30 89).

[0066] 2. The call is directed to a voice platform (VPF) with voicerecognition functions.

[0067] 3. The VPF broadcasts a message prompting the caller to speak hisidentifier.

[0068] 4. The caller speaks the three (for example) literal expressionsof his identifier (Sesame—Open—Pinocchio).

[0069] 5. The VPF recognizes the literal expressions from the lists ofliteral expressions drawn up beforehand and determines the card to whichthe call is to be billed.

[0070] 6. The VPF interrogates the card base to verify that theidentifier recognized matches an existing and active card.

[0071] 7. The card base sends back an authorization and details of therights of the card concerned.

[0072] 8. The VPF broadcasts a message prompting the caller to enter thenumber of a called party.

[0073] 9. The caller enters the number of a called party.

[0074] 10. The call is set up.

1. A method of identifying a caller with a telephone service operator,which method is characterized in that it comprises the following steps:for the operator, drawing up at least one list of literal expressionsand allocating the caller an identifier consisting of a combination ofconsecutive literal expressions taken from each of said lists, for thecaller, connecting to said telephone service and speaking, in order,each literal expression of said combination, and for the operator,identifying the caller by searching a database for the identity of thecaller allocated the combination of literal expressions spoken by thecaller and recognized by the operator.
 2. An identification methodaccording to claim 1, characterized in that an authentication key isassociated with said identifier and the caller supplies saidauthentication key after speaking the combination of literal expressionsallocated to him.
 3. An identification method according to claim 2,characterized in that said authentication key is a plurality of digitsentered in DTMF code.
 4. An identification method according to claim 2,characterized in that said authentication key is another literalexpression recorded by the caller the first time he connects to thetelephone service.
 5. An identification method according to claim 2,characterized in that said authentication key is a voiceprint of thecaller established when said combination of literal expressions isspoken.
 6. An identification method according to claims 3 and 5,characterized in that a double authentication key is associated withsaid identifier and comprises a main key consisting of a voiceprint anda back-up key consisting of a plurality of digits entered in DTMF code.7. An identification method according to any one of claims 1 to 6,characterized in that a list of literal expressions is established byassociating a category with each literal expression of a given list andassociating with each category a list of literal expressions from whichthe next literal expression is taken.
 8. A prepaid telephone cardcharacterized in that it includes an identifier consisting of one ormore literal expressions to be spoken by a caller to identify himselfwith a telephone service operator by an identification method accordingto any one of claims 1 to
 7. 9. A prepaid telephone card according toclaim 8, characterized in that it also contains an authentication key.